Heart disease is a significant public health problem. Therefore, in medicine, it is of considerable value to obtain cross-sectional and volumetric images of the human heart. Applications include angiography of coronary vessels for detecting stenosis, examination of the thoracic aorta for dissection of the vessel wall, and quantization of calcium deposits in the coronary arteries as a marker for atheroscerotic plaque.
Recently, this last application has gathered significant interest due to the finding that the exam can be performed with a conventional high-speed helical CT (Computer Tomography) scanner, as opposed to the more expensive and less prevalent electron beam CT scanner. However, helical CT scanners are still too slow to “freeze” the motion of the heart, resulting in some cross-sectional images being blurred and out of register with other images captured at a different phase of the heart's cycle of contraction (systole) and relaxation (diastole).
As a consequence, methods have been introduced to determine the heart cycle phase of axial CT images by simultaneously recording the electrocardiogram (EKG), and synchronizing this signal with the sequence of images. Since the high amplitude “r-wave” of the EKG is a reliable and very brief indicator of the onset of ventricular contraction, it is straightforward to use its peak as an indicator of when heart motion will be near its most violent. It is then possible to either shut down image acquisition during these times, or retrospectively eliminate images that have been acquired at these times. This method is called EKG gating.
The disadvantage of EKG gating is that it significantly lengthens the exam time due to the need to wire the patient with electrodes, etc. It also introduces additional complications in the design of the CT scanner and of the software used to post-process the acquired images. It may additionally require manual verification of the selection of images, and introduces the possibility of mismatching EKG traces and images from different patients.
As a result, there is a need in the art for systems and methods that can filter images acquired during an image scan of a patient without the need for external monitoring devices such as EKG monitors.